Transition elements color

Color Centers. Characteristics of a color center (1,3,7) include production by irradiation and destmction by heating. Exposure to light or even merely time in the dark may be sufficient to destroy these centers. Color arises from light absorption either from an electron missing from a normally occupied position, ie, a hole color center, or from an extra electron, ie, an electron color center. If the electron is a valence electron of a transition element, the term color center is not usually used. 

Other Transition Element Perchlorates. Both divalent and trivalent manganese perchlorate compounds [13770-16-6 13498-03-8] are known. Perchlorates of Fe, Co, Ni, Rh, and Pd have been produced as colored crystals (70—72). 

Vanadium, a typical transition element, displays weU-cliaractetized valence states of 2—5 in solid compounds and in solutions. Valence states of —1 and 0 may occur in solid compounds, eg, the carbonyl and certain complexes. In oxidation state 5, vanadium is diamagnetic and forms colorless, pale yeUow, or red compounds. In lower oxidation states, the presence of one or more 3d electrons, usually unpaired, results in paramagnetic and colored compounds. All compounds of vanadium having unpaired electrons are colored, but because the absorption spectra may be complex, a specific color does not necessarily correspond to a particular oxidation state. As an illustration, vanadium(IV) oxy salts are generally blue, whereas vanadium(IV) chloride is deep red. Differences over the valence range of 2—5 are shown in Table 2. The stmcture of vanadium compounds has been discussed (6,7). 

Quinoxaline-2,3-dithione (2,3-dimercaptoquinoxaline) (90) forms chelates with several transition elements and is used as a colorimetric agent for the detection and quantitative estimation of nickeT and also for the quantitative estimation of palladium. " Nickel gives a pink coloration with (90) in ammoniacal solution, and palladium an orange-red color in AA-dimethylformamide solution containing a little hydrochloric acid. Spectrophotometric studies of the chelate compounds of (90) with Ni(II), Co(II), and Pd(II) in alkaline solu-... 

B Main group elements are in the A families, while transition elements are in the B families. Metals, nonmetals, metalloids, and noble gases are color coded in the periodic table inside the front cover. 

Transition metals tend to have higher melting points than representative metals. Because they are metals, transition elements have relatively low ionization energies. Ions of transition metals often are colored in aqueous solution. Because they are metals and thus readily form cations, they have negative standard reduction potentials. Their compounds often have unpaired electrons because of the diversity of -electron configurations, and thus, they often are paramagnetic. Consequently, the correct answers are (c) and (e). 

The first evidence that post-transition elements, the metals especially, could be reduced to highly colored anions was published over 90 years ago by Joannls (O who discovered that sodium and lead or their alloys dissolve In liquid ammonia to yield an Intensely green-colored solute. A stoichiometry of 2.25 lead atoms per sodium ( ) for what was evidently an anion led Kraus ( ) to formulate this as Pbg ". Until the past decade the principal Information regarding this and many other species were the stoichiometries obtained by Zintl and coworkers from... 

Many of the compounds formed by transition elements appear in various colors. Several are very toxic. Chromium, zinc, cobalt, nickel, and titanium are carcinogenic. 

Element Ionic radii Transition elements Ionic radii Absorption (color) Emission Rare earths Ionic radii Emission... 

In many inorganic pigments, lanthanides and transition elements are responsible for color. Metal oxides and oxide hydroxides are, however, also important as colored pigments because of their optical properties, low price, and ready availability. Colored pigments based on oxides and oxide hydroxides are either composed of a single component or mixed phases. In the latter, color is obtained by incorporation of appropriate cations. 

Most Phase I oxidations are performed by cytochrome P-450. "Cytochrome," derived from Greek, literally means "colored substance in the cell." The color is derived from the properties of the outer electrons of the transition element iron. "P-450" denotes a reddish pigment with the unusual property of having its major optical absorption peak (Soret maximum) at about 450 nm, when it has been reduced and combined with carbon monoxide.330 Although the name "P-450" was intended to be temporary (until more was known about the substance), the terminology has persisted for 18 yr because of the increasing complexity of this enzyme system and because of the lack of agreement on new nomenclature. 

Iron is a nonamphoteric, transition element with the ability to exist in two oxidation states—Fe2+ (ferrous) and Fe3+ (ferric). A positive reaction to alkaline ferric chloride is an indication of the presence of hydroxyl groups with which Fe2+ forms colored complexes. Stable copper and iron chelates... 

Out of the multiplicity of catalytic processes, Roginskii has segregated two large groups (1) those processes characterized by electronic transitions and (2) those in which the acidic properties of the catalyst are important. Thus more restrictive conditions on the nature of the process make it possible to associate the catalytic activity with certain physical attributes such as color, electrical conductivity, and electron affinity. Consequently a number of simple rules for the selection of catalysts can be stated. The following characteristics have been noted (1) pronounced effects are noted with highly colored compounds (2) catalysts containing transition elements are exceptionally active and (3) white compounds do not have a pronounced catalytic effect. 

C Transition elements are famous for their multiple oxidation states and colors. Compounds containing iron are usually reddish in color (hemoglobin and rust are examples). 

The colors associated with many compounds of the transition elements arise from electronic transitions, that... 

Chlorine dioxide is an odd molecule that is, a molecule containing an odd number of electrons. It was pointed out by G. N. L.ewis in 19J6 that odd molecules (other than those containing transition elements) are rare, and that they are usually colored and are always paramagnetic (attracted by a magnet). Every electronic structure that can bjC written for chlorine dioxide contains one unpaired electron. This unpaired electron presumably resonates among the three atoms, the electronic structure of the molecule being a resonance hybrid ... 

Have you ever wondered what produces the gorgeous colors in a stained-glass window or in the rubies, emeralds, and sapphires mounted on a ring Compounds of transition elements are responsible for creating the entire spectrum of colors. 

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